The present invention relates to research laboratory equipment and, particularly, to a novel and improved laminar diffuser for use with a metabolic cage for collecting and separating feces and urine excreted by laboratory animals.
Many laboratory experiments require the use of laboratory animals of varying sizes and types, such as mice and rats. The laboratory animals are kept in isolated environments, known as metabolic cage units, wherein their intake of food and water is carefully measured and controlled. Additionally, in such experiments, it is necessary to collect excreted material from the laboratory animals, and it is often necessary to separate that material into solid (fecal) and liquid (urine) components. Collection of separate samples of feces and urine requires essentially complete separation of the excreted material, preferably as it is produced.
One type of metabolic cage unit which attempts to separate feces and urine is manufactured and sold under the trademark NALGENE by the Nagle Company of Rochester, N.Y. This device includes a cage in which a laboratory animal, usually a rodent, is retained. The cage includes means for providing food and water to the rodent. A wire bottom permits excreted material to pass freely. The excreted material falls onto an inverted cone, which is intended to act as a separator of the feces and urine. A globe having a conductive tube at its bottom surrounds the cone. The conductive tube opens slightly from top to bottom having therefor the appearance of an inverted funnel, and is connected to a urine ring. The urine ring, in turn, is connected to a urine collection tube. A feces collection tube is suspended in the middle of the lower end of the conductive tube.
In theory, at least, feces bounce off the cone, and then down and around the globe toward the conductive tube. The feces should then bounce free of the globe, and fall into the intended collection tube. The urine, is intended to flow along the diverging surface of the cone, to drip onto the interior surface of the globe, and to continue to flow along the interior surface of the globe until it reaches the upper end of the conductive tube, which, as stated, opens downwardly therefrom. Due to the high viscosity of the urine, it should continue to flow along the diverging interior surface of the conductive tube, even through the conductive tube is open directly underneath the flow surface, and be entrained along the interior surface of the conductive tube until it reaches the urine collecting ring, whence it is delivered to the urine collecting tube.
This separation technique relies on the theoretic perception that rodent feces are usually quite hard, and almost pellet-like, and so bounce freely off the hard surfaces of the unit, while the high-viscosity liquid urine flows along the interior of the conductive tube. However, in practice, the separation obtained by such a structure is less than completely satisfactory because a substantial amount of mixing of urine and feces occurs.
Another known configuration is described in U.S. Pat. No. 3,227,139, and manufactured by Maryland Plastics, Inc., of Federalsburg, Md., under the trademark ECONO-METABOLISM UNIT. This configuration includes a cage having food and water for the rodent retained therein. The bottom of the cage is a wire mesh positioned over a collection funnel. Suspended in the middle of the funnel is an inverted cone, which does not serve as a separator, but instead prevents any excreted material from falling directly through the opening of the funnel. The opening of the funnel leads to a bulb suspended therebeneath. A urine collection receptacle is positioned below the bulb.
The operation of this device is similar to that of the NALGENE device, in that the excreted material is directed to the bulb and, in theory, the feces bounce off the bulb, while the urine flows along its surface to the urine collection receptacle. The feces are then intended to bounce to an open area, from which they may be collected, while the urine is collected in the desired receptacle.
The practical operation of this configuration is also lacking, since it does not always collect all the urine in the urine collection receptacle, and some feces may fall therein. Additionally, during prolonged or excessive urination, the urine does not flow continually along the bottom of the bulb, but splashes into the feces collection area. While this device may work satisfactorily with a small mouse, it is unsatisfactory with a larger laboratory animal, such as a large (150 gram) rat, due to the relatively high volume of urine excreted by such laboratory animals.